1. Field of the Invention
The invention relates to a wire or cable, and more particularly to a fire-resistant wire or cable having an fire-resistant insulation layer or a fire-resistant outer sheath.
2. Description of the Related Art
Fire resistant or fire retardant materials can be used as architectural or decorative materials. Architectural materials disclosed in Taiwan Patent Nos. 583,078 and 397,885 primarily comprise a stacked layer, serving as a fire resistant layer, comprising nonflammable inorganic materials such as pearlite (or perlite), MgCl2, MgO, CaCO3 or cement. In addition, a stiff fire resistant laminate can be obtained from flexible substrates made of fibers or non-wovens blended with flame retardants, foaming agents and 50˜80 inorganic materials by weight.
Fire resistant coatings, serving as decorative materials, disclosed in Taiwan Patent Nos. 442,549, 499,469 and 419,514 comprise a combination of foaming and intumescent agents, carbonization agents, flame retardants, and adhesives which foam and intumesce when exposed to fire. U.S. Pat. No. 5,723,515 discloses a fire-retardant coating material including a fluid intumescent base material having a foaming agent, a blowing agent, a charring agent, a binding agent, a solvent, and a pigment, for increasing resistance to cracking and shrinking. A compound disclosed by U.S. Pat. No. 5,218,027 is manufactured from a composition of a copolymer or terpolymer, a low modulus polymer, and a synthetic hydrocarbon elastomer. The fire retardant additive comprising a group I, group II or group III metal hydroxide with the proviso that at least 1% by weight of the composition is in the form of an organopolysiloxane. U.S. Pat. No. 6,262,161 relates to filled interpolymer compositions of ethylene and/or alpha-olefin/vinyl or vinylidene monomers, showing improved performance when exposed to fire or ignition sources, and fabricated articles thereof. The articles are often in the form of a film, sheet, a multilayered structure, a floor, wall, or ceiling covering, foams, fibers, electrical devices, or wire and cable assemblies.
EP Patent No. 10330569, JP Patent No. 7211153, KR Patent No. 9201723B and EP Patent No. 0029234 disclose an outer sheath of wire or cable comprising polyvinyl chloride (PVC). Further, EP Patent No. 0769789 and U.S. Pat. No. 5,891,571 disclose mixing the polyvinyl chloride with calcium salt, zinc salt, magnesium salt, aluminum salt, phosphate, hologenated plasticize, aluminum hydroxide, zinc stannate to increase the flame retardant property. Moreover, JP Patent No. 1041112 discloses an outer sheath comprising the copolymer ethylene-PVC with ethylene vinyl acetate-PVC.
Due to the inferior electrical insulation characteristics of PVC, a novel insulation layer or an outer sheath of fire-resistant wire or cable is called for. U.S. Pat. No. 6,303,681(B1), U.S. Pat. No. 5,166,250, JP Patent No. 2000191845, US Patent No. 20060148939, and CA Patent No. 2210057 disclose mixing the polypropylene (or polyethylene) with metal oxide. JP Patent No. 2005322474 disclose mixing the copolymer of EVA with styrene-ethylene-butylene and Mg(OH)2 to fabricate the insulation layer or an outer sheath of metal wire. US Patent No. 20050205290 discloses mixing the HDPE and borax glass to improve the flame retardant property of the fire-resistant wire. Conventional flame retardant polymer compositions are obtained by physical bending of organic polymer and inorganic flame retardant, wherein coupling agents or surfactants are typically incorporated to improve the dispersity of inorganic flame retardant. However, because the organic polymer does not react with inorganic component to form a well-structured composite by the formation of chemical bonds, the conventional flame retardant compositions easily melt, ignite, or produce flaming drops under exposure to flame or ignition sources.